This would be either a bug in python 2.5 or a new check in glibc (since it
doesn't happen on FC6), especially on 64bit platform. Or it could be in one of
the binary modules from skencil itself, but I don't see the dump hinting at
something like this. How could one find out?

Since this happens in the python interpreter itself, I would say this is a
python bug. At least I don't see any of the skencil native modules involved.
However, it would be interesting to see when the error occurs. You would have to
step through the python code using "python -m pdb
/usr/lib/skencil-0.6.17/skencil.py".

Try to comment out the line
check_for_shm_images(widget)
in the procedure InitFromWidget in the file graphics.py.
If that works we could disable shared memory, at least for
that platform. Does it crash also on non-64-bit?